The present invention pertains to gas filtration and more particularly to a device for filtering ventilation air which has inlet air damping and distribution means.
Various types of ventilating air filtering and distribution devices having inlet air distribution means are known. However, the heretofore known devices have the air distribution means attached at the air inlet to the device. The attachment structure, thus, interferes with the flow of incoming air creating an undesireable pressure drop and an air flow turbulence at the inlet.
Further, the prior art devices have done little to eliminate non-uniform, or sharp, outlet air velocity profiles as measured across the outlet from the device. A uniform outlet air velocity profile is important in order to maintain a laminar air flow in an area served by the ventilating device.
Further, some prior art ventilating air filtering and distribution devices use a two piece butterfly-type damper located in the air inlet. This butterfly-type damper requires a relatively complicated and, therefore, expensive worm gear to actuate the two pieces of the valve.
In some applications, the butterfly damper is oriented to open by having the two pieces thereof pivot inwardly or into the inlet. It has been known to occur, when subjected to high incoming air velocities, that the butterfly damper is blown to a closed position, thus, potentially causing damage to the ventilating system due to the sudden creation of high pressure blockages in the system.
In other applications, the butterfly damper mentioned above has been reoriented to open by having the two pieces thereof pivot outwardly of the inlet, thus, solving the problem of the damper being blown to a closed position when subjected to high incoming air velocities. However, when oriented to openby having the two pieces pivot outwardly of the inlet, the damper can be blown to an open position when subjected to a high inlet air velocity. While this orientation limits potential damage to the ventilating system caused by high pressure blockages when the damper is blown closed, it will result in destroying a balanced laminar air flow into the room being ventilated.
Another prior art ventilating air distribution device is disclosed in U.S. Pat. No. 3,818,815, issued on June 25, 1974 to Thomas L. Day. This patent discloses a hood-like stucture having an inlet duct and an air discharge outlet. Two identical perforated plates are sandwiched together and mounted to one end of an adjustment shaft. The adjustment shaft is coaxially disposed relative to the inlet duct and is threadably mounted at its other end to a plate disposed in and attached to the inlet duct. The perforated plates are larger than the inlet duct and are mounted to the shaft for selective transverse movement relative to the axis of the shaft. A drawback of this device is that the shaft mounting plate being disposed in and attached to the inlet duct interferes with the incoming air flow creating a turbulence and an undesireable pressure drop. Additionally, this device does little to create a uniform outlet air velocity profile across the outlet. Indeed, depending upon the lateral locations of the perforated plates relative to the inlet duct a non-uniform outlet air velocity profile would be encouraged.